In FY2009 7 subjects with a first lower extremity deep vein thrombosis (DVT) of less than two weeks duration were enrolled and treated with low dose tPA given by pulse spray catheter delivery directly into the clot. This brought the total accrual for the study from 23 subjects (since the inception of the study in 2004) to 30 subjects out of a maximum accrual limit of 30. For each subject on the protocol venographic and ultrasound studies were used to document the presence of a DVT. tPA was administered at a maximum daily dose of up to 10 mg for up to four consecutive days (maximum total dose 40 mg).Venographic studies were done at the end of the inpatient hospitalization and showed restored patency in all subjects. Demographics of subjects enrolled to this date show 18 male and 12 female subjects with a mean age of 46 years (range 18 to 62 year). One third (33%) had underlying prothrombotic mutations of coagulation factor V (8/30 FVLeiden) or prothrombin (2/30 prothrombin 20210). ATIII deficiency was seen in two patients in our study. Baseline laboratory studies showed mean pre-treatment functional tPA of 1 IU/mL, and mean PAI-1 levels of 8 IU/mL. At the close of the first thrombolytic treatment, the mean tPA reached a peak of 75 IU/mL and mean PAI-1 levels were 0.1 IU/mL. By 1 hour post-procedure, the mean tPA level was 4 IU/mL and the mean PAI-1 level was 5 IU/mL. Subsequent time points for tPA showed mean levels of 1 IU/mL, 0.4 IU/mL, and 0.2 IU/mL at 2, 4, and 8 hours, respectively. Subsequent time points for PAI-1 showed mean levels of 9, 14, and 30 IU/mL at 2, 4, and 8 hours, respectively. The data indicate that the tPA levels were largely gone by 1 hour post-Rx, and gone entirely by 2 hours post-Rx. PAI-1 levels disappeared coincident with peak tPA levels, and were half-recovered by one hour post-Rx, and back to baseline by 2 hrs post-Rx. Interestingly, PAI-1 levels were 175% of baseline at 4 hours post-Rx, and 375% of baseline 8 hours post-Rx, indicating an overshoot after administration of tPA. Results of venography show 100% patency at discharge and at 6 weeks in 5 of the 7 new subjects studied; two new patients have not reached the six week time point at the time of this report. One subject with varicose veins had recurrent thrombosis off anticoagulation and was re-treated with tPA to open his obstructed veins. Three patients had minor bleeding attributable to the tPA treatment. In summary, low dose tPA administered via pulse-spray catheter to subjects with a first acute DVT had overall good outcomes with respect to immediate patency of treated vessels (97% of 30 patients treated to date), and had no major bleeding complications attributable to tPA administration. The apparent safety of this approach is likely due in part to the relatively low doses of tPA employed and perhaps to the affinity of tPA for fibrin clot. Future plan: This study has reached its accrual limit, an no more patients will be enrolled. We will describe the findings and conclusions of our work in the next fiscal year. We contemplate future studies of tPA at time points later than 2 weeks after symptoms, or treatment with the thrombolytic enzyme plasmin itself to extend the interval in which treatment can be initiated.